The present invention is directed generally to electromagnetic interference noise suppression. More particularly, the invention concerns connector structure that suppresses, to an acceptable level, emanation of any electromagnetic interference radiation onto unshielded wiring used to interconnect elements of a data processing system.
As the clock rates of today's data processing systems increase, so do the problems of attenuating or suppressing electromagnetic interference noise radiated by the equipment of the systems. Suppression techniques include shielding the equipment by properly constructed enclosures. When, as is often the case, the data processing system is made up of several separate data processing units (e.g., a host processor to which is coupled a plurality of workstations, printers, disk storage units, and the like), the wiring that is used to interconnect the data processing pieces can act as an antenna to carry out and radiate electromagnetic interference noise that may be produced by the interconnected units.
Recognizing the problems that can be created by such radiation, the Federal Communications Commission (FCC) and other (international) agencies have set standards limiting the amount of electromagnetic interference radiation that equipment can produce. Manufacturers of data processing systems, therefore, presently make every attempt to design their systems with electromagnetic interference noise radiation suppression in mind. Thus, cabinets and enclosures for data processing systems are designed, for example, to act both as a shield and to form a connecting point for DC returns. Signalling communicated from a unit of the system to another is carried by shielded wiring. Although these techniques are effective, problems continue to exist.
One problem is that the use of shielded wiring is costly, particularly when considered for use in large data processing networks (e.g., local area networks), both in terms of expense of the wiring itself, and the labor to install the network interconnections. Perhaps more importantly, local area networks are often preferably installed with the interconnect wiring part of the building construction in order to preclude the wiring from being exposed in travelled areas. Frequently, buildings, particularly those that may be newly constructed, will have installed twisted-wire pair wiring for telephones or for local area network interconnections. In order to comply with FCC (and other) limits on electromagnetic radiation limits, the twisted-wire pair wiring must be removed in favor of replacement with shielded wiring. Now, the expense includes the structural modifications encountered in such replacement, a not particularly attractive approach.
One solution has been to attach ferrite beads on the wiring, near each of the connectors. This solution finds some attenuation of the EMI noise, but not always enough.
Accordingly, there is a need for a form of EMI noise suppression in use in connection with unshielded twisted wire pairs used to interconnect data processing equipment.